RESUMO
The purpose of this investigation was directed to propose sensitive, accurate and reproducible methods of analysis that can be applied to determine distigmine bromide (DTB), cyclopentolate hydrochloride (CPHC), diaveridine hydrochloride (DVHC) and tetrahydrozoline hydrochloride (THHC) drugs in pure form and pharmaceutical preparations via charge-transfer complex formation with 7,7,8,8-tetracyanoquinodimethane (TCNQ) and tetracyanoethylene (TCNE) reagents. Spectrophotometric method involve the addition a known excess of TCNQ or TCNE reagents to DTB, CPHC, DVHC and THHC drugs in acetonitrile, followed by the measurement of the absorbance of the CT complexes at the selected wavelength. The reaction stoichiometry is found to be 1:1 [drug]: [TCNQ or TCNE]. The absorbance is found to increase linearly with concentration of the drugs under investigation which is corroborated by the correlation coefficients of 0.9954-0.9981. The system obeys Beer's law for 6-400, 20-500, 1-180 and 60-560 µg mL(-1) and 80-600, 10-300, 1-60 and 80-640 µg mL(-1) for DTB, CPHC, DVHC and THHC drugs using TCNQ and TCNE reagents, respectively. The apparent molar absorptivity, sandell sensitivity, the limits of detection and quantification are also reported for the spectrophotometric method. Intra- and inter-day precision and accuracy of the method were evaluated as per ICH guidelines. The method was successfully applied to the assay of DTB, CPHC, DVHC and THHC drugs in formulations and the results were compared with those of a reference method by applying Student's t and F-tests. No interference was observed from common pharmaceutical excipients.